1. Technical Field
The present invention relates to a blue light-emitting compound and an organic electroluminescent device comprising the compound. More specifically, the present invention relates to a blue light-emitting compound that can be used to fabricate an organic electroluminescent device with improved color purity of blue emission and excellent life characteristics, and an organic electroluminescent device fabricated using the blue light-emitting compound.
2. Background Art
As displays have become larger in size in recent years, there is an increasing demand for flat panel display devices that take up as little space as possible. Liquid crystal display devices as representative flat panel display devices can be reduced in weight when compared to the prior art cathode ray tubes (CRTs), but have several disadvantages in that the viewing angle is limited, the use of backlight is inevitably required, etc. Organic light-emitting diodes (OLEDs) as a novel type of flat panel display devices are self-emissive display devices. Organic light-emitting diodes have a broad viewing angle, and are advantageous in terms of light weight, small thickness, small size and rapid response time when compared to liquid crystal display devices.
A representative organic light-emitting diode was reported by Gurnee in 1969 (U.S. Pat. Nos. 3,172,862 and 3,173,050). However, this organic light-emitting diode suffers from limitations in its applications because of its limited performance. Since Eastman Kodak Co. reported multilayer organic light-emitting diodes in 1987 (C. W. Tang et al., Appl. Phys. Lett., 51, 913 (1987); and J. Applied Phys., 65, 3610 (1989)), remarkable progress has been made in the development of organic light-emitting diodes capable of overcoming the problems of the prior art devices.
Organic electroluminescent devices have superior characteristics, such as low driving voltage (e.g., 10V or less), broad viewing angle, rapid response time and high contrast, over plasma display panels (PDPs) and inorganic electroluminescent display devices. Based on these advantages, organic electroluminescent devices can be used as pixels of graphic displays, television image displays and surface light sources. In addition, organic electroluminescent devices can be fabricated on flexible transparent substrates, can be reduced in thickness and weight, and have good color representation. Therefore, organic electroluminescent devices are recognized as promising devices for use in next-generation flat panel displays (FPDs).
Such organic electroluminescent devices comprise a first electrode as a hole injection electrode (anode), a second electrode as an electron injection electrode (cathode), and an organic light-emitting layer disposed between the anode and the cathode wherein electrons injected from the cathode and holes injected from the anode combine with each other in the organic light-emitting layer to form electron-hole pairs (excitons), and then the excitons fall from the excited state to the ground state and decay to emit light. Organic electroluminescent devices have been applied to full-color displays. To obtain fill colors, it is necessary to arrange pixels, which emit light of three primary colors, i.e. green, red and blue colors, respectively, on a panel. Various methods have been suggested to arrange pixels on a panel. Examples of such methods include: (i) the arrangement of three types of organic electroluminescent devices emitting blue, green and red colors, respectively; (ii) the separation of light emitted from a white (a mixed color of red, green and blue (RGB) colors) light-emitting device into three primary colors through a color filter; and (iii) the use of light emitted from a blue organic light-emitting device as a source of fluorescence emission to convert the light to green and red light.
One important requirement is to provide a material capable of emitting blue light with high luminance, high efficiency and improved color purity. Hence, intensive researches have been made. For example, U.S. Pat. No. 6,455,720 describes a 2,2-(diaryl)vinylphosphine compound as a blue light-emitting material. Further, Korean Patent Laid-open Publication No. 10-2002-0070333 describes a blue light-emitting compound which has a diphenylanthracene structure in the center and an aryl-substituted specific structure at an end thereof, and an organic electroluminescent device using the blue light-emitting compound. However, the organic electroluminescent devices including the materials have insufficient luminescence efficiency and luminance.
Further, Korean Patent No. 525,408 discloses an organic electroluminescent device which uses a pyrene compound substituted with a diphenylamine derivative. This organic electroluminescent device, however, has poor color purity of blue emission (i.e., chromaticity coordinates of x=0.146 and y=0.205), which makes it difficult to achieve deep blue light emission and be applied for full-color displays producing natural colors.
Additionally, U.S. Pat. No. 5,153,073 discloses an organic electroluminescent device which uses a pyrene compound substituted with a diphenylamine derivative. However, this device substantially emits bluish green light due to its poor color purity of blue emission, and partially emits bluish light with low luminance.
Also, PCT Publication No. WO 2004/083162 A1 discloses an organic electroluminescent device which uses a pyrene compound substituted with a diphenylamine derivative. However, this device has poor color purity of blue emission and is not suitable for the manufacture of full-color displays producing natural colors.
Further, PCT Publication No. WO 2005/108348 A1 discloses an aromatic amine derivative having a structure in which a pyrene compound is directly substituted with a substituted or unsubstituted diphenylamine group. However, the aromatic amine derivative emits bluish green light due to the presence of an aryl or alkyl group directly bonded to the pyrene ring.
There is thus a need for a novel blue light-emitting compound and an organic electroluminescent device comprising the compound.
The information disclosed in this Background section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.